The present invention relates to copper alloys and copper alloy conductors. Copper has long been the main material used to conduct electricity. Various copper alloys have been developed to overcome shortcomings of elemental copper such as low strength and flexure life. High strength and flexure life, consistent with maintaining high conductivity, are important requirements for many applications. Cadmium copper (alloy C 16200) and cadmium-chromium-copper (alloy C 18135) have been two of the traditional copper alloys used as conductors where higher strength has been required. These alloys increase the strength of copper with a minimal reduction in its electrical conductivity, an important balance for conductor alloys. However, due to the hazardous nature of cadmium and restrictions imposed on materials containing this element, substitute alloys have been developed to replace cadmium containing alloys. The prior art also comprises the Percon 24 brand copper alloy wires made by the owner of the present invention and described in its U.S. Pat. Nos. 6,053,994 and 6,063,217, based on a common patent application filing of Sep. 12, 1997. Those wires are cadmium free yet, similar to alloy C18135, meet the ASTM B624 standards and have a composition of 0.15-1.30 weight percent (w/o) chromium, 0.01-0.15 w/o zirconium, balance copper and are specially processed as described and claimed in the '217 patent.
The art also includes examples of alloys of copper with cobalt, phosphorus, nickel, silicon, chromium including combinations often coupled with highly specialized processing requirements showing efforts to advance the art in the decade since the Percon 24 patents, as shown, e.g., in PCT published applications: WO2009/123159 ('159) (copper alloy conductor with nickel, silicon, tin, magnesium and zinc); WO 2009/123137 ('137) (Cu—Ni—Si—Co—Cr); WO 2009/11922 (Cu—Co—P—Sn with oxygen control) and WO 2009/049201 (Cu—Sn—Ni—P) optionally with special processing “at the expense of yield” to increase formability.
Alloy C17510, a beryllium copper alloy, is yet a stronger alloy than alloy C18135 with further reduction in electrical conductivity. This alloy is used to either reduce the conductor size or improve flexure life. Electrical conductivity and tensile strength for elemental copper and the C18135 and C17510 alloys are summarized below in Table 1. Required properties for alloy C18135 are outlined in the ASTM B 624 standard specification. Properties for C17510 in conductor are listed in U.S. Pat. No. 4,727,002.
TABLE 1Properties of State of the Art Conductor AlloysAlloyElectrical Conductivity, % IACSTensile Strength, ksiCopper10035C181358560C175106395
FIG. 1 (prior art) shows, increasing strength is associated with a decrease in electrical conductivity, i.e., these two characteristics are inversely related. The reduction in electrical conductivity with increased strength limits the use of a conductor due to increased resistance. Also, when higher strength and flexure life are required a larger and heavier conductor has to be employed to provide sufficient cross-section and load bearing capacity.
Therefore it is beneficial to obtain an alloy usable for conductors with high strength and high flexure life without sacrificing electrical conductivity or with minimal sacrifice to electrical conductivity. ASTM B 624 describes a set of properties which have been found quite useful in aerospace, medical, electronics and other applications. These properties are defined as 60 ksi tensile strength and 85% IACS electrical conductivity.
It is a main objective of the present invention to provide an environmentally friendly alloy meeting the 85% IACS electrical conductivity standard while providing an 80 to 85 ksi tensile strength, an increase of at least 33% in strength compared to prior art high strength copper alloys.
It is a further object of the invention to simplify processing of the material and obtain high yield, more cost efficient copper alloy production in wire and other forms, particularly without special control of oxygen or other interstitials content beyond customary metal fabrication good practices.